The present invention relates to utility knives and more particularly, to utility knives which include an ergonomically-shaped handle and a retractable blade.
In many utility knives, a replaceable blade or one continuous blade is fixed at one end of a knife handle. Prior art utility knives often included blades that were constantly exposed which posed a danger to people or objects that came into contact with the knife while not in use. These prior art designs often required disassembly of a two-piece knife handle in order to remove and replace a worn blade. Disassembly required additional tools was cumbersome, and risked the loss or damage of handle fastening screws and other component parts. Another design for a utility knife incorporated the use of one continuous blade. Utility knives of this type generally lack safety features and involve the use of a less structurally stable blade. The aforementioned limitations have the effect of decreasing overall utility and operator convenience. The following patents are incorporated herein by reference as background information with regard to utility knives heretofore available: U.S. Pat. No. 3,906,627 to Manning; U.S. Pat. No. 5,426,855 to Keklak; and U.S. Pat. No. 4,615,118 to Ihata.
One example of a utility knife of the prior art which attempts to overcome the aforementioned problems is shown in the patent to Manning, and generally comprises a utility knife which includes a retractable working blade. Many of these types of knives utilize a manually-operated thumb screw which requires loosening, manual sliding, and retightening in order to allow the working blade to extend beyond the handle end. Other models utilize a thumb lever which requires depression and sliding along a channel in the handle in order to extend the blade beyond the handle. Once the working blade is placed in the extended position, the blade remains fixed and subsequently acquires the inherent danger of having an exposed knife blade while the utility knife is not in use. These models also retain the cumbersome requirement of disassembling the two-piece knife handle in order to remove and replace a worn blade.
Another example of a utility knife of the prior art which attempts to overcome the aforementioned problems is shown in the patent to Keklak, and generally comprises a utility knife which includes the use of an automatically retractable blade. This patent and similar types of utility knives include the use of a spring-biased working blade which is automatically retractable into the knife handle upon release of the operating lever. In the Keklak patent, a toggle linkage is mounted between a fixed point in the handle and the blade holder. A spring which normally biases the blade holder rearwardly can be overcome when the operator squeezes a lever protruding from the bottom of the handle which results in extension of the toggle linkage, which forces the blade to its exposed position. The Keklak patent also includes a mechanism for limiting the extension of the blade by manually positioning a thumb screw which inhibits the extension of the toggle linkage. The Keklak structure does not allow one to replace a worn blade without manually separating the pieces of the handle which requires additional tools, time, and handling. All of these factors make blade replacement cumbersome.
Another version of a utility knife incorporates the use of a continuous blade which is extendable beyond the handle by either loosening or depressing a thumb screw and sliding the thumb screw along a channel in the handle. An example of this type of utility knife is described in the patent to Ihata. Typically, the continuous blade includes parallel scoring lines at predetermined intervals along the face of the blade. The scoring is used to break off the worn blade tip section which is subsequently replaced with a new section of blade tip. This version of a utility knife lacks the safety feature of an automatically retractable blade, and also typically is embodied by a non-ergonomically designed handle. In addition, the method for replacing the end of the working blade, by means of breaking off the worn tip, presents a danger of blade tips inadvertently bouncing into the air. The continuous blade also involves the use of a less structurally sound blade, resulting in decreased utility.
Consequently, there remains a need for a utility knife which is simple, inexpensive, with fewer component parts, and which overcomes the aforementioned problems. The present invention provides such a device.
Accordingly, an object of the invention is to provide a safety utility knife with a permanently sealed handle and a self-retracting working blade.
Another object of the invention is to provide a safety utility knife with an ergonomically shaped handle.
A further object of the invention is to provide dual levers for moving the working blade between a retracted (inoperative) position and an extended (operative) position.
Yet another object of the invention is to provide a utility knife having storage of extra replacement blades in the handle, and to enable replacement of a worn working blade with a replacement blade without the use of additional tools.
In accordance with the invention, a utility knife is provided which is particularly adapted to extend a working blade to the cutting position upon squeezing a pair of levers against the handle. The utility knife comprises a handle having a cavity and a forward opening, a bottom opening, a top opening, and a rear opening. A bottom release lever is pivotally mounted to the handle and movable with respect to the handle within the bottom opening. A top drive lever is pivotally mounted to the handle and movable with respect to the handle. A working blade holder is slidably disposed within the cavity of the handle and supports a working blade which is movable with respect to the handle within the forward opening. A spring biased toggle linkage connects to the working blade holder and the handle. The spring biased toggle linkage is adapted to extend upon pivoting of said top drive lever toward said handle. An extra blade holder is slidably mounted to the handle and movable with respect to the handle within the rear opening and includes a front support end for engagement with the working blade. Slidable displacement of the extra blade holder outward from the handle disengages the support end from the working blade and allows removal of the working blade from the utility knife. Once the working blade is unrestrained, an operator can easily remove and replace it with one of the extra blades.
In accordance with another aspect of the invention, a utility knife is provided which comprises a handle having a cavity. A bottom release lever is pivotally mounted to the handle and movable with respect to the handle within the cavity. A top drive lever is pivotally mounted to the handle and movable with respect to the handle. The handle includes a forward opening and a rear opening and a working blade holder slidably disposed within the handle. A working blade is supported by the working blade holder. A spring biased toggle linkage is connected to the working blade holder and the handle and is adapted to extend upon pivoting of the top drive lever toward the handle. An extra blade holder slidably mounted to the handle and movable with respect to the handle within the cavity. The extra blade holder has a slot for storing extra blades and includes a front support end for engagement with the working blade. Slidable displacement of the extra blade holder disengages the support end from the working blade and allows removal of the working blade from the utility knife.